(to the original poster) Keep in mind some plants you get from a Nursery may be sterile , and not produce fruit, but only flowers.
I have seen them here (-20 F/ -28c) grow , and flower when I was a kid, but never went back or noticed to see the fruit later.
I would think they would grow also mulch or compost wouldn't hurt 1 or 2 feet thick
or growing on the south side of a wall to retain heat
(but if they die to the ground I do not see a need ,
but I see a lot of plants not rated for zone 5 growing here all the time,
but need babying for a couple years to get established.
(if you look at sheffields seed catalog they say they have a seed source from Minnesota
that information is listed under the picture) it may be true but the things are aggressive so I wouldn't be surprised.